JPH03119041A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To obtain a rubber composition suitable for tire tread parts with high responsiveness by blending a raw material rubber composed of high-vinyl polybutadiene rubber, natural rubber and high-cis polybutadiene rubber with specific carbon black and petroleum-based softener. CONSTITUTION:A composition, obtained by blending 100 pts.wt. raw material rubber composed of (A) 30-80 pts.wt. polybutadiene rubber with >=70wt.% 1,2-vinyl content, (B) 10-50 pts.wt. natural rubber and (C) 10-40 pts.wt. polybutadiene rubber containing >=95wt.% cis-1,4-bonds with (D) 80-130 pts.wt. carbon black having >=100m<2>/g nitrogen specific surface area and a small particle diameter and (E) 20-90 pts.wt. petroleum-based softener with 0.9-0.98 viscosity specific gravity constant, having <=500MPa shearing storage elastic modulus at -30 deg.C and <=15 difference in hardness between 60 deg.C and -10 deg.C and suitable as especially tread parts of all season tires.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rubber composition for trend tires that has stable maneuverability over a wide temperature range and also has excellent grip on snowy and icy road surfaces.

[Conventional technology]

Traditionally, the performance requirements for automobile tires include safety, economy, ride comfort, etc. In particular, with the development of expressway networks, cornering characteristics during high-speed driving of vehicles,
There is a desire for tires with improved maneuverability and safety such as braking performance, but in recent years there has also been a demand for tires that have excellent responsiveness, so to speak, that accurately follow the driver's intentions.

As a measure to improve tire motion performance, particularly grip performance, it is important to increase the frictional force with the road surface by increasing the hysteresis loss of the tread rubber. That is, the tread surface that is in friction with the road surface is deformed at high speed due to minute irregularities on the road surface, and the greater the energy dissipation due to hysteresis loss that occurs during this periodic deformation process, the greater the frictional force becomes. Moreover, since the deformation on the friction surface is extremely fast, Williams
It is known that the Landelf-Eri temperature-time conversion law depends more on the hysteresis loss measured at the tire temperature than on the temperature at which the tire is used. In fact, tan δ (loss coefficient), which is a measure of hysteresis loss, shows a good correlation with the coefficient of friction of a tire. Involved. Conventionally, in order to increase the hysteresis loss of a rubber composition, a method of compounding a rubber with a high glass transition temperature (Tg) such as a high styrene-containing styrene-butadiene copolymer rubber (SBR) has been used. . This is because the tan δ of rubber has a peak around T8, so by bringing the tan δ peak closer to the temperature range that is involved in friction performance (equivalent to 0°C if the tire running temperature is 30°C). This is intended to utilize a high tan δ.

Figure 1 shows emulsion polymerized styrene with different styrene contents.
This figure shows the jan δ temperature dependence of butadiene copolymer rubber. When the styrene content increases, the tan δ peak temperature moves to the high temperature side, and the tan δ value increases near 0° C., which is the base of the tan δ peak. However, at the same time, the temperature dependence of tan δ also increases around 0°C, and therefore the grip performance of the tire also changes greatly depending on the environmental temperature.Furthermore, the elastic modulus also sharply changes in response to the tan δ peak. Changes to

In other words, as the temperature decreases, the elastic modulus increases rapidly, making it impossible for the rubber to follow the unevenness of the road surface, or in the case of waterways, etc., the rubber cannot deform at all.
There was a problem in that maneuverability and braking performance deteriorated.

On the other hand, when using a polymer with a low Tg, such as high-cis butadiene rubber (BR), the grip performance at low temperatures improves, but on the other hand, the tan δ around 0°C decreases, and the grip performance at high temperatures decreases. A contradiction arises in that the grip ability is insufficient. Therefore, attempts have been made to harmonize the above-mentioned antinomy by blending different types of polymers called SBR/BR or by incorporating large amounts of small particle size carbon (D, F, Moore"T
he Fr1ction of Pneumatic
Tyres'', Elasevier Scientific
ic Publishing Company 197
5+ U, S.

Patent No. 4,748,168+Unexamined Japanese Patent Publication No. 1983
-12932 etc.).

Furthermore, JP-A-62-260843, JP-A-62
Publication No. 190238 utilizes the compatibility of these blended polymers and delicate control of Tg to successfully exhibit all-weather resistance from high to low temperatures.

However, since such rubber exhibits properties intermediate to those of the blended polymers, it cannot take full advantage of the inherent strengths of the constituent polymers, and has the disadvantage that neither high-temperature nor low-temperature grips are completely satisfactory. In addition, incorporating a large amount of small particle size carbon has problems in processability and increases heat generation.

As a measure to deal with this trade-off,
-66733 and JP-A-62-62840 disclose a technique of adding a low-temperature plasticizer to these blended polymers, but although the low-temperature grip is certainly improved, the rubber elastic modulus decreases at high temperatures. The decline is significant,
The handling stability at high temperatures is not always satisfactory.

The goal of these technologies is to improve the all-weather performance of tires, and tread rubber is suitable for all-weather, high-performance tires that pursue the ultimate performance. However, in recent years, the performance required of tires is not only high grip for handling performance.
There is a need for tires that accurately respond to the driver's intentions. In other words, the demands for automobile tires must be at odds with the social demands for automobiles, but with recent advances in ergonomics and electronics engineering, automobiles have not only superior acceleration performance and cornering performance; Does not cause discomfort to people's sensibilities,
There is a demand for cars that, like well-made shoes, do not make you feel that there are tires on them. This requires tires that respond to the intentions of the driver of the vehicle without any phase delay.

If we were to call these tires high-responsive tires, they would generate lateral force without any time delay when the driver of the vehicle turns the steering wheel, that is, they would have excellent responsiveness to slight steering. is necessary.

That is, in addition to the conventional all-weather performance, the high-responsive tire needs to have excellent responsiveness even when the steering angle is small. From this perspective, we investigated the factors that delay the response at small steering angles and found that in addition to the tire structure, the trend rubber and the phase lag of the tread block part have an effect.

As an index of phase lag, hardness at 60°C and -10
It can be expressed as the difference in hardness in °C. In other words, the conclusion is that the rubber with a larger difference in hardness has a faster stress relaxation rate, and as a result, stress attenuation occurs more easily in response to minute deformations in the tread, making it impossible to maintain a predetermined stress, resulting in poorer micro-steering response. was obtained.

As shown in Figure 1, the difference between the hardness at 60°C and the hardness at -10°C (hereinafter referred to as coefficient M) is greater for emulsion-polymerized styrene-butadiene copolymer rubber with a higher Tg and high styrene content. big. That is, if a styrene-butadiene copolymer rubber with a high Tg is used to improve grip performance, the coefficient M also increases, resulting in poor responsiveness.

After careful consideration to resolve these contradictions, we found that
The tread rubber composition of the present invention has been achieved. in this way,
There are no known examples in which trend rubber compositions have been studied from the viewpoint of tire responsiveness, and therefore the technology of the present invention is completely new.

[Problem to be solved by the invention]

The present invention provides an all-season type high-responsive (small coefficient M) rubber composition for tire treads, which has stable maneuverability over a wide temperature range and also has excellent grip on snowy and icy road surfaces. The purpose is to

[Means to solve the problem]

The present inventors have developed polybutadiene rubber by increasing the absolute value of tan δ in the temperature range involved in friction and by increasing the coefficient M.
As a result of extensive research into rubber compositions that reduce the We have discovered what can be achieved and arrived at the present invention.

Therefore, the rubber composition for tire tread of the present invention is
30 to 80 parts by weight of polybutadiene rubber (A) with a 1,2-vinyl content of 70% by weight or more, and 10 to 5 parts by weight of natural rubber.
0 parts by weight, and 10 to 40 parts by weight of polybutadiene rubber (B) containing 95% by weight or more of cis 1.4-bonds to form a raw material rubber with a total rubber amount of 100 parts by weight. Nitrogen specific surface area x00ff per part by weight
1/g or more, and 20 to 90 parts by weight of a petroleum-based softener having a viscosity specific gravity constant of 0.90 to 0.98, and can be stored under shear at -30°C. The elastic modulus is 500 MPa or less, and the difference between hardness at 60°C and -10°C is 15
It is characterized by the following:

This means will be explained in detail below.

fil raw rubber.

30 to 80 parts by weight of polybutadiene rubber (A), 10 to 50 parts by weight of natural rubber, and polybutadiene rubber (B)
The total amount of rubber is 100 parts by weight.

(al　Polybutadiene rubber (A).

1.2-High vinyl BR with a vinyl content of 70% by weight or more
It is.

If the 1.2-vinyl content is less than 70%, the TgM of the polybutadiene rubber will be too low, resulting in a decrease in tan δ at 0° C., resulting in poor grip. 1. A higher 2-vinyl content is desirable, but for manufacturing reasons 9
The upper limit is about 5% by weight. The appropriate amount of this polybutadiene rubber (A) is 30 to 80 parts by weight. 3
This is because if it is less than 0 parts by weight, the properties of polybutadiene rubber will not be exhibited, and if it exceeds 80 parts by weight, the rubber strength will not be sufficient and it will be unsuitable for use as a tire tread rubber.

(bl natural rubber.

Blending natural rubber with polybutadiene rubber is important from a practical standpoint.

This is because automobile tires can be used not only on paved roads, but also on rough roads.
There will be opportunities to drive on uneven roads, and in such cases, blending natural rubber can reduce tread damage caused by sudden external forces such as chipping and cuts. requires a blending amount of 10 parts by weight or more.On the other hand, if the blending amount of natural rubber is too large, the essential properties of polybutadiene rubber will be diluted and the grip performance will deteriorate. ,
It is necessary to suppress the blending amount to 50 parts by weight or less.

(C) Polybutadiene rubber (B).

High cis B containing 95% by weight or more of cis 1,4-bonds
It is R. Formulated to improve low temperature performance and wear resistance. The amount required is 10 to 40 parts by weight; if it is less than 10 parts by weight, no improvement in low temperature performance and wear resistance can be expected;
Grip performance is poor when the weight exceeds the weight range.

(2) Carbon black.

Furthermore, in order to be put to practical use as a tread for automobile tires, it must have sufficient performance in terms of wear resistance and handling stability. In order to improve steering stability to a level suitable for high-performance tires, the nitrogen specific surface area must be 100r.
It is necessary to mix 80 parts by weight or more of small particle size carbon blanks with a particle size of rf/g or more with respect to 100 parts by weight of the raw material rubber. However, if it exceeds 130 parts by weight, the abrasion resistance and heat generation properties will be extremely poor, so the content must be 130 parts by weight or less.

(3) Petroleum-based softener (extension oil).

Other characteristics of tires include ride comfort, noise, and braking performance, and in order to improve these performances, it is also necessary to add extender oil to improve processability during tire manufacturing. If the viscosity specific gravity constant of the extender oil is less than 0.90, no improvement in braking performance will be observed, and if it exceeds 0.98, the processability due to the softening effect will not be improved. For this reason, 0.90~
The range is 0.98. Note that it is desirable to use an aromatic extender oil of about 0.98. It is necessary to adjust the trend rubber elastic modulus by appropriately increasing or decreasing the blending amount of extender oil depending on the blending amount of carbon black. However, if it is less than 20 parts by weight per 100 parts by weight of the raw material rubber, the compounded rubber will not elongate, resulting in poor chipping and cutting properties.
It is also difficult to process, so it is not preferred. On the other hand, if it exceeds 90 parts by weight, the strength will decrease and the abrasion resistance will become extremely poor, making it difficult to put it into practical use.

(4) The rubber composition formed by blending the carbon blank and the petroleum softener with the raw rubber as described above needs to have a shear storage modulus of 500 MPa or less at 30°C. Generally, a rubbery substance is in a glass state at a temperature below Tg, and its elastic modulus is more than 100 times that at room temperature, making it brittle and breaking at the slightest strain. The temperature at this time is called the low-temperature embrittlement temperature, and is known as an indicator of the low-temperature performance of rubber materials. However, when the temperature change in the elastic modulus is gradual as in the case of the rubber composition according to the present invention, the embrittlement temperature cannot be simply estimated from Tg. This is a plot of the low temperature embrittlement temperature and the shear storage modulus (G') at that temperature. From this, it can be seen that the G' value at the embrittlement temperature of all the samples exceeds 500 MPa.

Therefore, if it is 500 MPa or less, it can be said that the embrittlement temperature is not exceeded. Furthermore, the reason why the shear storage modulus is set at -30°C is that tires are not normally used at temperatures lower than -30°C.

Note that this shear modulus is measured using a dynamic torsion tester at a strain of 0.5% and a frequency of 20 Hz.

Furthermore, in order to improve the responsiveness at the time of a small steering angle, it is better that the difference (coefficient M) between the hardness at 60° C. and the hardness at -10° C. is small. If this difference is 16 or more, for example, even if the tire has tread rubber with good grip performance, the evaluation of response will be poor, and as a result, the steering stability evaluation of the tire as a whole will be poor. .

If it is 15 or less, it has sufficient performance as a highly responsive tire, but it is more preferably 13 or less. The hardness at this time is measured according to JIS K 6301.

For reference, a rubber composition obtained by blending such high vinyl content rubber with diene rubber such as natural rubber and polybutadiene rubber is disclosed in JP-A-56-1107.
This technology is known from Japanese Patent No. 53, but because the emphasis is on achieving both low drying resistance and wet grip, changes in hardness due to temperature are not considered, and the amount of carbon black blended is also small. Therefore, it is not suitable as a high-response, high-performance tire.

Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Example 1 Polybutadiene rubber having the components shown in Table 1 was produced. Furthermore, these rubbers and emulsion polymerized SBR for comparison were vulcanized according to the formulations shown in Table 2.The numbers in Table 0 are parts by weight unless otherwise specified. Vulcanization conditions were 160 x 20 minutes;
A rubber sheet with a thickness of 2 mm was obtained. The physical properties of this sheet were measured. In addition, the measurements in the examples were performed by the following method.

The vinyl bond amount was determined by the Morello method.

Shear modulus σ at -30℃ (-30℃) and 0℃
The tan δ in RHEO? fETIiI
Using a dynamic viscoelasticity measuring device manufactured by C5, frequency 20) 1z
, measured at a shear strain of 0.5%. Hs is JIS 6301
Hardness according to

(Margins below this page) Turtle”L hawk D The amount of polymer blended in the table excludes the amount of oil.

-1 emulsification ((H synthesis styrene-butadiene copolymer rubber:
Nippon Zeon il N1pol 1721゜1 Emulsified IR
1-polymer styrene-butadiene copolymer rubber: Nippon Zeon@
N1pol 9520°"3 N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine.

"St" 3R (11, (2) oil extended fraction (37,5j
flll(g) was totaled.

” N-Cyclohexyl-2-benzothiazolylsulfenamide.

As can be seen from Table 2, Comparative Example 4.5 is emulsion polymerized SBR.
This is an example. The formulation of Comparative Example 5 has good low temperature performance, but low tan δ (0°C) and poor grip performance. On the contrary, in Comparative Example 4, the tan δ (0° C.) is high, but the low temperature performance is poor. Comparative Example 1 uses polybutadiene rubber whose 1,2-vinyl content is out of the range of the present invention,
This is an example of a blend of natural rubber and high-cis 1,4-polybutadiene rubber, and although the coefficient M is small and good, the tan δ at 0° C. is low and the grip performance is poor. Comparative Example 2 is an emulsion polymerized SBR with a bound styrene content of 35% by weight.
This is a blend example, but the tan δ at 0°C is low, and
Since the coefficient M is also large, it is expected that the responsiveness will be poor.

Comparative Example 6 is an example in which 50 parts by weight of polybutadiene rubber with a cis-1,4-bond content of 98% by weight was blended.
The tan δ is low, and the grip performance is poor.

Compared to these, Examples 1 and 2, which satisfy the scope of the present invention, have well-balanced performance.

Example 2 Tread rubber was made using the formulations of Example 1 and Comparative Example 4 in Table 2, and tires were made and a handling stability test was conducted. The evaluation was divided into fine rudder response and limit performance, and testers evaluated the feeling of each. The results are shown in Table 3. Third
As can be seen from the table, although the tire having the tread of the rubber composition of Example 1 was inferior to Comparative Example 4 in marginal performance, it was proven to have excellent fine steering response and excellent overall evaluation.

〔Effect of the invention〕

As explained above, the rubber composition of the present invention has more stable grip performance and steering response over a wide temperature range than conventional technologies, and also has excellent grip on snowy and icy road surfaces. It can be suitably used for pneumatic tire treads, especially all-season type high-responsive tire treads.

[Brief explanation of drawings]

Figure 1 shows the ta of emulsion polymerized SBR that differs only in styrene content.
An explanatory diagram showing that the nδ-temperature curve shows that the peak temperature is higher when the styrene content is high. Figure 2 is an explanatory diagram showing the relationship between the low-temperature embrittlement temperature and shear modulus of a rubber compound. . Note) (Domestic 5-seater sedan, tire size 195/65R15)
The evaluation score is out of 10, the higher the better.

Claims (1)

[Claims] 30 to 80 parts by weight of polybutadiene rubber (A) with a 1,2-vinyl content of 70% by weight or more, and 10 to 5 parts by weight of natural rubber.
A raw material rubber with a total rubber amount of 100 parts by weight is composed of 10 to 40 parts by weight of polybutadiene rubber (B) containing 0 parts by weight and 95 parts by weight or more of cis-1,4-bonds, and 100 parts by weight of this raw material rubber. Whereas, nitrogen specific surface area is 100m^
2/g or more and 20 to 90 parts by weight of a petroleum softener having a viscosity specific gravity constant of 0.90 to 0.98. Shear storage at -30°C The elastic modulus is 500 MPa or less and the difference between hardness at 60°C and hardness at -10°C is 15
A rubber composition for a tire tread characterized by the following: